RomFS

Overview

RomFS or Read-Only Filesystem is part of the NCCH format, and is used as external file storage.

RomFS can be used:

• in conjunction with the ExeFS of a NCCH

• to contain the game manual accessible from the Home Menu

• to contain the DLP Child CIA

• or to contain game cartridge update data

(There may be more implementations in the future)

Format

All of the content (including the header) in RomFS appears to be aligned to 0x1000 byte blocks, the first block starts at 0x1000. Starting with the second block, every block begins with a SHA-256 hash. This hashes the whole 0x1000-byte block following this block. For the last block, this hash hashes the first block at 0x1000. The total RomFS filesize is always at least 0x4000.

The RomFS header is 0x80 bytes long and following is known about the structure:

START	SIZE	DESCRIPTION
0x00	0x4	Magic "IVFC"
0x04	0x4	Magic number 0x10000
0x14	0x4	2nd content size
0x1C	0x4	Level 1 block size, in log2.
0x2C	0x4	3rd content size
0x34	0x4	Level 2 block size, in log2.
0x44	0x4	Main (1st) content size
0x34	0x4	Level 3 block size, in log2.
0x60	0x20	Second block hash

The block hash from the header hashes the second block at 0x2000.